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Not Applicable.
The present invention relates to lamps. More particularly, the present invention relates to multi-filament lamps. Generally, inside the glass envelope or bulb of a lamp, a filament, which is usually made from tungsten, is extended between two power terminals. Basically, the filament is a resistor that heats up when a voltage is applied across the terminals, and normally operates at temperatures of about 2500xc2x0 C. in incandescent lamps, and at significantly higher temperatures in halogen lamps. At these high temperatures the filament gives off a substantial amount of thermal radiation, which includes a considerable amount of visible light (when compared to the amount of visible light given off at lower operating temperatures). Also, these high temperatures cause some of the tungsten molecules to evaporate off of the filament and condense onto the glass bulb. This causes the filament to become thinner and more resistant to current flow, causing the thinner filament portion to become even hotter, and leading to further evaporation. Similarly, fabrication inefficiencies can also cause thin spots to be formed on the filament during manufacturing. Eventually, the loss of tungsten molecules will cause the filament to fail or xe2x80x9cburnoutxe2x80x9d and, due to the economics involved, an inoperable lamp is generally replaced and disposed of without expending any effort toward repair.
To extend the life of electric bulbs (or lamps), various methods have been employed to minimize, or compensate for, the loss of filament molecules. For example, incandescent bulbs are oftentimes filled with an inert gasxe2x80x94instead of operating the filaments in a partial vacuum inside of the bulb. Besides preventing filament combustion, the inert gas is a source of molecules that are used to collide with the evaporated tungsten molecules. Desirably, prior to the tungsten molecules condensing on the inside of the glass bulb, these collisions will redirect the tungsten molecules back toward the filament where they may be recovered. As another example, halogen lamps minimize the loss of tungsten filament molecules through the use of a process known as halogen recycling. Generally, halogen recycling is a chemical reaction that collects previously free tungsten molecules from the inside surface of the glass and then, due to the high temperature of the filament, re-deposits them on the filament.
A different approach to extending lamp life makes use of more than one filament. In this regard, multi-filament lamps have been described in a number of patents, for example, U.S. Pat. No. 4,553,066, issued to Fields et al. on Nov. 12, 1985, describes a multi-filament lamp that uses longitudinally extending filaments and a wire grid to help ensure that a failed filament does not break free and interfere with an operable filament. This invention, however, supplies power to each filament separately and, therefore, uses a separate lead-in wire for each filament, e.g., a three-filament lamp will require three lead-in wires and a common wire. Since the amount of time that a lamp is energized is the main cause of lamp failure, and since all of the filaments are simultaneously operating in this invention, lamp life may not be appreciably extended. In the U.S. Pat. No. 5,061,879, issued to Munoz et al. on Oct. 29, 1991, another multi-filament lamp is described. This invention, however, does not power each filament at the same time, but, on the other hand, this invention is only a two-filament lamp and it requires the use of an external control module for switching the second filament on after the first filament fails.
Furthermore, while light bulbs generally last for several hundred hours before burning out, some light bulbs will last much longer and are commonly referred to as xe2x80x9clong lifexe2x80x9d bulbs. Generally, long life bulbs are made with a single, heavier gauge, filament and have a reduced resistance to current flow, but these bulbs are not as economical as standard bulbs and like standard bulbs must be replaced as soon as their single, heavier gauge filament fails. Thus, a need still remains for an economical way to extend the life of a light bulb.
According to its major aspects and briefly recited, the present invention is light bulb having at least two groups of filament segments and at least three filaments wherein, each group of filaments can be classified as primary filaments, which are a part of a series connected electrical circuit and, therefore, capable of initially being energized to provide illumination; backup (or secondary, or primary backup) filaments, which bypass a failed, i.e., open circuited, primary filament and become a part of the series circuit and, therefore, capable of being energized to provide illumination; and/or other subsequent level filaments (or subsequent level backups), which, in turn, bypass a failed, i.e., open circuited, prior level filament and become a part of the series circuit and, therefore, subsequently capable of being energized to provide illumination. Generally, filaments are fabricated by forming tungsten into a very fine wire having a diameter of about 50 microns, and then winding this wire into a double spiral coil and attaching the ends of the filament to power leads, which are attached to a support structure made of an insulator such as glass. Oftentimes, when a filament burns out, i.e., open circuits, it does so in one place along the length of the filament while the remainder of the filament is still usable, if this remaining operable portion could be connected back into an operable filament circuit. By using a two-filament group embodiment, containing a total of three filaments, as an example, but not as a limitation, two of the three filaments are primary filaments and are initially capable of providing illumination when the lamp is energized, and the other filament is a backup (or secondary) filament to one of the primary filaments. Since any of the embodiments of the present invention can be made to use filaments having the same, or different, electrical and/or luminosity characteristics, in this example it is assumed that one of the primary filaments is a lower gauge filament, is operating hotter, and/or is otherwise more likely to fail prior to the other primary filament. The secondary filament, in this example, through the use of shunts is connected in parallel with the more likely to fail filament. The shunts may include, but are not limited to, devices that are made of an oxidized metallic material, which does not become conductive until a breakdown voltage greater than the material""s breakdown voltage rating is applied to it. In normal operation this magnitude of voltage, i.e., greater than the breakdown voltage rating, is not applied across the shunts, but upon failure of the primary filament to which the shunts are attached (which, in this example, is the more likely to fail filament) a voltage greater then the breakdown voltage rating is applied across the shunts and the backup filament becomes electrically connected in series with the operable primary filament, i.e., the backup filament bypasses the failed primary filament. Similarly, other embodiments of the present invention lamp may include, but are not limited to, those that have a separate backup filament across each of the primary filaments, which would allow for a separate backup filament to be used to bypass each failed primary filament, and/or at least one tertiary filament across at least one of the backup filaments, which will be used to bypass a failed, i.e., open circuited, backup filament and, therefore, become a part of the series filament circuit and, therefore, capable of being energized to provide illumination.
The primary filament segments are connected in series and can be positioned in an essentially straight configuration, in a semi-circular ring, or as an array, while the backup and/or subsequent level filament segments are also connected in series and are offset, or are spaced away, from their primary (or prior level) filament segment counterparts. The primary, the backup, and/or the other subsequent level, filament segments are preferably connected to support structures that are built within the interior of the lamp; however, the primary filament segments may be directly connected to these support structures while the backup (and/or the other subsequent level) filament segments are indirectly connected to these structures by being attached to the primary filament segments (and/or the other prior level filament segments) through stand-offs (or other similar support devices). Generally, each end of the series of primary filament segments is attached to a power lead (or other lead-in conductor), and each individual primary filament segment that has an associated backup filament segment, upon becoming open circuited, uses shunts to provide an electrical connection to their associated backup (or secondary) filament segment and the power leadsxe2x80x94either directly or through other primary and/or backup filament segments. Similarly, when a backup (or secondary) filament segment becomes open circuited it also uses shunts to provide an electrical connection to its associated backup, which is a second-level backup (or a tertiary) filament segment.
Additionally, the backup (or secondary) filament segments may have a higher resistance than their associated primary filament segments to provide for proper shunt operation. Moreover, the backup (or secondary) filament segments are designed to provide the user with a visual indication that primary filament segments have failed before the entire system of filament segments becomes inoperative, i.e., the backup (or secondary) filament segments can be dimmer (or brighter) than the primary filament segments. Similarly, subsequent level filament segments will have a higher resistance than their prior level filament segments for the same purposes.
A feature of the present invention is the use of at least one backup (or secondary) filament segment. When the primary filament segment to which the backup (or secondary) filament segment burns out, the light will continue to operate by using the backup (or secondary) filament segment in place of the failed primary filament segment. Not only does the backup (or secondary) filament segment extend the usable life of the lamp, but, through the use of a number of groups, segments and/or backups, e.g., tertiary filament segments acting as second-level backups to backup (or secondary) filament segments, etc., the life of the lamp may be increased by a factor much greater than two while still maintaining high visible light emission efficiency. Generally, visible light emission efficiency is exchanged for long-life in most current xe2x80x9clong-lifexe2x80x9d lamps. Related to this, the increased lifetime also reduces the time and cost of changing light bulbs by the same factor. Therefore, even allowing for a somewhat higher manufacturing cost for the present invention multiple, parallel filament lamp, the overall cost savings of the present lamp compared to prior art lamps may be significant.
Another feature of the present invention is the use of bypass shunts. Essentially the bypass shunts are located within the interior of the glass envelope surrounding the filaments and are used as switches to turn on the backup filaments when a filament burns out. Because the bypass shunts and the additional filaments are located within the interior of the present invention lamp, the present invention lamp can be used in standard light sockets without having to make modifications to the lamp or the lamp socket.
Still another feature of the present invention is the use of the open circuit voltage across a failed filament to activate a shunt in order to switch on a backup filament. This feature enables the backup filaments to operate sequentially and automatically on the failure of an associated filament.
Other features and their advantages will be apparent to those skilled in the art of lamp design from a careful reading of a Detailed Description Of Preferred Embodiment accompanied by the following drawings.